It is easy enough to link portrait and body pictures for your slaves (to avoid confusion, i know how to add portait for the main), but I can't seem to find one for the "master". Am I missing something or there is no such feature. To be honest its more annoying than necessary but still.

Yes, I just realised I misspelled main in the title. My main language isn't english, sorry.

If I am understanding you right you want to add a body image for the player character. The only way I have found to do that is to go to the portrait selection for the player character and click assign both at the bottom right of the selection panel. Then as long as you have a body image with the same name and under the same folder sets as the portrait image it will set both the portrait and the body to that image.